Graphite-Based Negative Electrodes: Correlation of Electrode Expansion and Cyclability

Silicon is the most attractive candidate to upgrade carbon as negative electrode material in lithium-ion batteries, due to its large specific charge and low reaction potential. However, the volume changes of silicon upon lithiation and delithiation lead to mechanical stress and poor performance, hindering the commercial use of silicon particles in lithium-ion battery negative electrodes. Many attempts to reduce the volume changes and achieve stable cyclability for silicon electrodes involve the use of carbon and/or graphite as electrochemically active matrix. Here we study the effect of silicon addition to graphite based electrodes and explore the differences in electrochemical response by means of in situ electrochemical dilatometry. Electrodes based on TIMCAL graphites, TIMREX® KS6 and TIMREX® SLP30, and silicon nanoparticles have been prepared by a simple mixture procedure and coated on Cu foil by standard doctor blade coating technique. Electrochemical performance and cycling stability of the composite electrodes was explored in coin type cells cycled in EC:DMC 1:1w:w, 1M LiPF 6 electrolyte using metallic lithium as counter electrode. Different parameters such as the nature of the binder, the effect of graphite morphology, and the use of electrolyte additives are studied in long term cycling experiments. The expansion of electrode layers was measured in a special dilatometry setup using three-electrode configuration, with both counter and reference electrodes of metallic lithium. A similar cycling program was used to explore the electrode’s expansion, however only during the first few cycles. Differences observed in the expansion of the composite electrode layers help us to understand the distinct electrochemical behaviour of each graphite based system, with and without silicon particles.